no numeric evaluation of ln(1) after replacing in ln(r/a) by r=a

Hello,

I couldn't find how to further simplify w in the example below. I'd
expect a result like  w_1+c_2*r_a^2+c_1 but not 
w_1+ln(1)*c_4*r_a^2+c_2*r_a^2+ln(1)*c_3+c_1

(%i2) w: c_1+c_2*r^2+c_3*ln(r/r_a)+c_4*r^2*ln(r/r_a)+w_1;
(%i45) w;
                          2     r             r          2
(%o45)         w_1 + c_4 r  ln(---) + c_3 ln(---) + c_2 r  + c_1
                               r_a           r_a
(%i46) ev(w,numer,r=r_a);
                                  2          2
(%o46)         w_1 + ln(1) c_4 r_a  + c_2 r_a  + ln(1) c_3 + c_1
(%i47)

Thanks for your help
Alain